1. Technical Field
This disclosure relates generally to mobile heat exchange systems and, more particularly, to sensor mounts for mobile refrigeration systems.
2. Background Information
Heat exchange systems are used to regulate internal environmental conditions in mobile units such as vehicles, trailers or shipping containers. For example, air temperature within a trailer transporting perishable goods (e.g., food, medication, etc.) is regulated to prevent spoilage and to maximize shelf life of the goods. Typically, such a heat exchange system includes a generator, a refrigeration unit having an evaporator, a return air duct, a supply air duct, a return air temperature (“RAT”) sensor and a controller. The evaporator is disposed between the return air duct and the supply air duct. The RAT sensor is mounted in the return air duct proximate the evaporator.
In operation, the RAT sensor measures the air temperature within the return air duct to estimate the air temperature within the trailer. The RAT sensor provides an output signal indicative of the measured air temperature to the controller. The controller compares the sensor output signal to a predetermined set point. When the sensor output signal indicates that the air temperature within the return air duct is greater than the predetermined value, the controller (in an on-cycle) turns the refrigeration unit on to cool the internal environment in the trailer. When the output signal indicates that the air temperature within the return air duct is less than the predetermined value, the controller (in an off-cycle) turns the refrigeration unit off to conserve energy and prevent over-cooling of the goods.
In theory, the refrigeration system is only turned on when air temperature within the trailer (estimated by the air temperature in the return air duct) is greater than or equal to the predetermined value. In practice, however, the air temperature in the return air duct does not always accurately estimate the air temperature within the trailer. For example, during the on-cycle, the generator provides power to the refrigeration unit. As a byproduct of providing power, the generator radiates and/or conducts thermal energy into the surrounding environment. Depending upon the configuration of the heat exchange unit, some of that thermal energy can increase the temperature of the air within the return air duct proximate the RAT sensor. In such a case, the signal from the RAT sensor would not accurately reflect the temperature conditions within the trailer. This temperature differential can lead to the refrigeration system remaining in the on-cycle for extended periods of time, even after the air temperature within the trailer has fallen below the predetermined temperature value. In another example, during the off-cycle, a heat buildup in the generator from sustained use may be radiated and/or conducted into the surrounding environment. This thermal energy can create a similar temperature differential such that the on-cycle is prematurely engaged; e.g., the air temperature proximate the RAT sensor increases above the predetermined value, while the air temperature within the trailer remains below the predetermined value. Disadvantageously, the temperature differential can (i) increase the number of on/off cycles per period, and (ii) increase the length of time the refrigeration unit is turned on, thereby increasing the cost of operating the heat exchange system.